1. Field of the invention
The invention relates to a liquid-cooled lance for blowing oxygen onto a steel bath for the purpose of refining it, and to a method of operating such a lance in a steel-making process. In particular, the invention relates to a liquid-cooled lance for blowing oxygen onto a bath of molten steel, having a tip with at least one outlet from which a primary supply of oxygen is blown onto the bath, a central duct for the supply of the primary oxygen surrounded by a double tube system for supply and removal of cooling fluid, a plurality of secondary outlets disposed around the lance in a conical widening of the lance axially spaced from the tip for blowing a secondary supply of oxygen and a plurality of secondary supply ducts extending along the lance for supply of the second oxygen to the secondary outlets.
2. Description of the prior art
U.S. Pat. No. 4,427,186 discloses a lance of the type described above. Another example of a lance which has secondary oxygen outlets (at least eight in number) is disclosed in GB-A-934112 but in this case the secondary outlets are all supplied from a single duct extending along the lance. U.S. Pat. No. 3,488,044 similarly shows four secondary oxygen outlets supplied via a single axially extending duct.
In steel-refining, the starting materials are often a mixture of liquid pig iron and scrap. The quantity of scrap which can be added, i.e. the scrap addition or scrap rate, is dependent among other things on the temperature of the liquid pig iron and on the quantity of heat evolved in the converter by the conversion of carbon into CO or CO.sub.2. The more CO.sub.2 is formed, the more heat is evolved, so that the scrap addition can be increased.
In some cases it can be an advantage to combine the steel process with an injection of gas through the bottom of the vessel into the liquid steel. For instance a better stirring effect is achieved thereby. Such a step may however cause a cooling of the bath, which reduces the amount of scrap which can be added. Particularly when the price of scrap is low it is desirable to have high flexibility to increase the amount of scrap added in the steel manufacture process. By making use of the secondary oxygen supply mentioned above, it is possible to supply extra heat to the bath so that extra scrap can be added and melted.